Shape Constraint Language

Transcription

1 Veronika Heimsbakk 24. april 2017

2 About us Håvard Veronika Both consultans at Acando Oslo Working with semantic technologies in public sector

3 Agenda 1. Terminology 2. What is SHACL? 3. Using SHACL for data validation 4. Validation result graphs 5. SPARQL processing 6. Demo

4 RDF graph An RDF graph is a set of triples. RDF triple An RDF triple consists of three components; subject, predicate and object.

5 RDF graph An RDF graph is a set of triples. RDF triple An RDF triple consists of three components; subject, predicate and object. subject is an IRI or a blank node.

6 RDF graph An RDF graph is a set of triples. RDF triple An RDF triple consists of three components; subject, predicate and object. subject is an IRI or a blank node. predicate is an IRI.

7 RDF graph An RDF graph is a set of triples. RDF triple An RDF triple consists of three components; subject, predicate and object. subject is an IRI or a blank node. predicate is an IRI. object is an IRI, literal or a blank node.

8 IRI (Internationalized Resource Identifier) within an RDF graph is a Unicode string with syntax defined in RFC3987. IRIs must be absolute, and may contain fragment identifier.

9 Shapes Constraint Language

10 A language for describing and validating RDF graphs. A vocabulary defined by a W3C working group. First revision in July Became a Candidate Recommendation 11th of April 2017.

11 sh:

12 The syntax of SHACL is the same as for any other RDF-based standard.

13 Today we will see both Turtle and JSON-LD.

14 Shapes

15 Shape Definition A shape is an IRI or blank node s that fulfills at least one of the following conditions in the shapes graph: s is a SHACL instance of sh:nodeshape or sh:propertyshape. s is subject of a triple that has sh:targetclass, sh:targetnode, sh:targetobjectsof or sh:targetsubjectsof as predicate. s is subject of a triple that has a parameter as predicate. s is a value of a shape-expecting, non-list-taking parameter such as sh:node, or a member of a SHACL list that is a value of a shape-expecting and list-taking parameter such as sh:or.

16 Node shape Definition A node shape is a shape in the shapes graph that is not the subject of a triple with sh:path as its predicate. SHACL instances of sh:nodeshape cannot have a value for the property sh:path.

17 Property shape Definition A property shape is a shape in the shapes graph that is the subject of a triple that has sh:path as its predicate. A shape has at most one value for sh:path. Each value of sh:path in a shape must be a well-formed SHACL property path. SHACL instances of sh:propertyshape have one value for the property sh:path.

18 It is recommended, but not required, for a node or property shape to be declared as a SHACL instance of sh:nodeshape or sh:propertyshape.

19 Building a shape ex:personshape a sh:nodeshape ; sh:targetclass ex:person.

20 Building a shape ex:namepropertyshape a sh:propertyshape ; sh:path ex:name ; sh:mincount 1.

21 Building a shape ex:personshape a sh:nodeshape ; sh:targetclass ex:person ; sh:property [ sh:path ex:name ; sh:mincount 1 ; ].

22 Severity sh:info sh:warning sh:violation A non-critical informative message. A non-critical constraint violation indicating a warning. A constraint violation.

23 Building a shape ex:personshape a sh:nodeshape ; sh:targetclass ex:person ; sh:property [ sh:path ex:name ; sh:mincount 1 ; sh:severity sh:violation ; ].

24 Focus node An RDF term that is validated against a shape using the triples from a data graph is called a focus node.

25 Value nodes The validators of most constraint components use the concept of value nodes, which is defined as follows: For node shapes the value nodes are the individual focus nodes, forming a set with exactly one member. For property shapes with a value for sh:path p the value nodes are the set of nodes in the data graph that can be reached from the focus node with the path mapping of p.

26 SHACL Core constraint components Value type Cardinality String-based Property pair Logical Shape-based Other

27 Value Type Constraint Components Used to restrict the type of value nodes. sh:class sh:datatype sh:nodekind Type of all value nodes. Values are IRIs. Datatype of all value nodes. Values are IRIs. At most one value for sh:datatype. Node kind of all value nodes. E.g. sh:literal.

28 Value Type Constraint Components ex:personshape a sh:nodeshape ; sh:property [ sh:path ex:name ; sh:datatype xsd:string ; ].

29 Cardinality Constraint Components Restriction on the number of value nodes for the given focus node. sh:mincount sh:maxcount Minimum cardinality. Maximum cardinality. Only for property shapes. At most one value, literal integer.

30 Cardinality Constraint Components ex:personshape a sh:nodeshape ; sh:property [ sh:path ex:name ; sh:mincount 1 ; sh:maxcount 1 ; ].

31 Value Range Constraint Components sh:minexclusive < sh:mininclusive <= sh:maxexclusive > sh:maxinclusive >=

32 String-based Constraint Components Specify conditions on the string representation of value nodes. sh:pattern sh:languagein A regex that all value nodes need to match. String literals, valid arguments for SPARQL REGEX function. SHACL list of allowed language tags for each value node. List members are string literals. sh:minlength, sh:maxlength, sh:uniquelang

33 String-based Constraint Components ex:personshape a sh:nodeshape ; sh:property [ sh:path ex:name ; sh:pattern "^V" ; ].

34 Property Pair Constraint Components Specify conditions on the sets of value nodes in relation to other properties. sh:equals sh:disjoint sh:lessthan sh:lessthanorequals

35 Logical Constraint Components Implement the common operators and, or, not and a variation of exclusive or. sh:not sh:and sh:or sh:xone

36 Shape Based Constraint Components Can be used to specify complex conditions by validating the value nodes against certain shapes. sh:node sh:property sh:qualifiedvalueshape sh:qualifiedmincount sh:qualifiedmaxcount

37 Other Constraint Components sh:closed sh:ignoredproperties sh:hasvalue sh:in

38 A node shape containing several property shapes ex:personshape a sh:nodeshape ; sh:property [ sh:path ex:name ; sh:datatype xsd:string ; sh:mincount 1 ; ] ; sh:property [ sh:path ex:age ; sh:datatype xsd:integer ; ]. After the lecture, I got a question about several property shapes. Here is an example of a node shape with two property shapes. Note that sh:path only may be declared once per property shape.

39 Validation Result Graphs Validation takes a data graph and a shapes graph as input and produces a validation report containing the results of the validation.

40 Shapes graph A shapes graph is an RDF graph containing zero or more shapes that is passed into a SHACL validation process so that a data graph can be validated against the shapes.

41 Data graph Any RDF graph can be a data graph.

42 Validation report The validation report is the result of the validation process that reports the conformance and the set of all validation results. The validation report is described with the SHACL Validation Report Vocabulary.

43 Example data graph ex:veronika a ex:person ; ex:age "25"^^xsd:integer ; ex:worksat ex:acando. ex:veronika ex:worksat a ex:age ex:person 25 ˆˆxsd:integer ex:acando ex:håvard a ex:person ; ex:age "Håvard" ; ex:worksat ex:acando. ex:håvard ex:worksat a ex:age ex:person Håvard. ex:acando

44 Example shapes graph ex:personshape a sh:nodeshape ; sh:targetclass ex:person ; sh:property [ sh:path ex:age ; sh:datatype xsd:integer ; sh:severity sh:violation ; ]. ex:personshape sh:property sh:targetclass a sh:path sh:datatype sh:severity ex:person sh:nodeshape ex:age xsd:integer sh:violation

45 Validation result graph [ a sh:validationreport ; sh:conforms false ; sh: result [ a sh:validationresult ; sh:resultseverity sh:violation ; sh:focusnode ex:håvard ; sh:resultpath ex:age ; sh:resultmessage "ex:age is expecting xsd:integer" ; sh:sourceconstraintcomponent sh:datatypeconstraintcomponent ; sh:sourceshape ex:personshape ; ] ].

46 sh:datatypeconstraintcomponent sh:sourceconstraintcomponent a sh:result sh:validationreport ex:age is expecting xsd:integer. sh:resultmessage ex:personshape sh:sourceshape a sh:validationresult sh:resultseverity sh:focusnode sh:resultpath sh:violation ex:håvard sh:conforms false ex:age

47 Summary Introducing constraints is important for data consistency, validation, quality and for making sense. Expressing constraints (SHACL) formal statements in predicate logic (OWL). May achieve SPARQL free validation.

48 More on SHACL breaking-news-last-shacl-made-cr-status-jan-voskuil shacl-the-next-generation-data-modeling-language/

49 Next up: Håvard & SPARQL processing